1. Field of the Invention
The present invention relates to multidimensional data encoding apparatus and decoding apparatus, and control method thereof.
2. Description of the Related Art
Image input/output devices such as a scanner, digital camera, printer, and the like respectively input or output images of their unique color spaces. Upon exchanging color image data between such devices having unique color spaces, a color profile which associates device-dependent colors with device-independent colors is used. As a format of color profiles, ICC profile defined by the International Colour Consortium (ICC) is well known.
In many cases, a color profile includes a color lookup table which associates two different color spaces with each other. Such color lookup table can be considered as multidimensional matrix data having a plurality of components. For example, a color lookup table which indicates correspondence between RGB colors of an input device and a device-independent standard color space such as Lab or the like is a multidimensional matrix of three dimensions and three components. Also, a color lookup table which associates the standard color space and CMYK data of an output device is a multidimensional matrix of three dimensions and four components. Furthermore, a color lookup table which indicates correspondence between CMYK and sRGB of a display device can be considered as a multidimensional matrix of four dimensions and three components.
In recent years, as color image devices gain higher accuracy, the data expression of elements of such color lookup table is increased from 8 bits to 16 bits. Not only a single mapping method between two color spaces is used, but also a plurality of mapping methods are defined to be selectively used as usage.
Upon distributing software for an image processing apparatus that applies color matching in correspondence with a plurality of input and output devices, corresponding color profile data need to be distributed together with that application.
As the number of color profiles increases, a large storage capacity is required upon storing the application software in storage media and distributing these media, or a long downloading time is required upon distributing the application software by downloading it on the Internet.
In consideration of such drawbacks, for example, Japanese Patent Laid-Open No. 11-17971 discloses a method of converting a color lookup table of each profile into one-dimensional (1D) data by zigzag-scanning it, and encoding differences from previous values by runlength, Huffman encoding, LZ encoding, or the like.
However, the compression ratio upon 1D conversion is not so high, and a compression method suited to a color lookup table has not been established yet.